A linear surgical stapling instrument includes a magazine for holding a plurality of undeformed surgical staples, and an upper jaw carrying the magazine and having opposed distal and proximal ends. An anvil is formed with staple-deforming pockets, and a lower jaw carries the anvil and has opposing distal and proximal ends respectively configured to mate with the distal and proximal ends of the upper jaw thereby to place the magazine and the anvil in confronting relation. A staple driver is carried in the upper jaw for driving staples held therein toward the anvil. Further, the upper and lower jaws are configured such that, when their respective distal and proximal ends are mated, a gap exists between the jaws in an intermediate region between their respective distal and proximal ends. Finally, a pivotably mounted clamp bar joins the upper and lower jaws and when actuated compresses them together in the intermediate region thereby to narrow the gap and to increase the clamping pressure between the magazine and the anvil. The instrument also includes a blocking system that prevents the jaws from being remated, once having been mated and having had staples in the magazine driven toward the anvil. Still further, the instrument includes a coupling device for coupling the jaws and clamp bar together when the staple driver is actuated.